1. Field of the Invention
This invention relates to a motor vehicle having an engine or an engine-gearbox unit encased within a noise-suppressing encapsulation.
2. Description of the Prior Art
The chief sources of noise emission in motor vehicles, such as lorries (e.g. trucks) and motor cars, are the exhaust system, the cooling air fan, the surface of the engine-gearbox unit, and, potentially, also the intake or aspiration system, the vehicle body and the tires. Since the exhaust system, the cooling air fan and the engine-gearbox unit contribute more or less in equal measures to the generation of noise, it is vital that any provisions which aim at a significant reduction of overall noise should cover all three of these main noise-generating sources. The expression "significant reduction of overall noise" is understood to imply a reduction of noise level of the order of 10 decibels (A) and over, which is desirable also in view of future legislation in this field.
Over the years various attempts have been made at reducing exhaust noise as well as for reducing the noise created by cooling air fans, normally involving the use of a rotor having aerodynamically correct design, and additionally to this, the provision of small rotor clearances and low pressure values.
It is also common practice to reduce noise radiation or emanation to the required degree from the engine and gearbox surfaces by providing a noise-suppressing overall casing, or cladding for these two units. In recent years a new construction system has been widely adopted for the design of sound-suppressing engine casings, wherein the engine and the gear box are closely encapsulated on all sides thereof by the sound-suppressing casing or cladding. This type of casing or cladding is distinguished by its comparatively slight additional weight and volume as compared with the open, i.e., unclad, unit. In these conventional arrangements the cladding, or casing, is supported from the engine-gearbox unit by means of body-resonance-absorbing elements. Such claddings are very acoustically effective even without further interior lining of sound-insulating materials, and as a rule they are ventilated by a separate fan unit associated therewith to avoid undue buildup of heat. Readily detachable access covers are normally provided in the maintenance or service areas for engine and gear box.
In spite of all the advantages presented by these conventional casings which are carried on the engine itself, certain problems arise in the special case of an engine-gearbox unit at certain points such as, for example, in the region between the engine and the vehicle frame or chassis and in the region of the engine bearings on the flywheel side, with respect to the accomodation and sealing of the sound-absorbing cladding. Further problems arise in the fitting or dismantling of sound-suppressed engines of this type in motor vehicles for major maintenance or service operations on the engine or gearbox, since the cladding cannot be fully dismantled on the vehicle, or only with great difficulty, i.e., without removing the driving unit as a whole.
These drawbacks are obviated in a further conventional arrangement which is described in SAE Paper 730,682, wherein the sound-suppressing casing, or cladding, is not supported from the engine but combined with the vehicle, the radiator-fan unit being arranged, as usual, in the vicinity of the engine. That is to say, in such cases within the sound-suppressing casing which comprises very large openings both at its front and rear ends to allow the full amount of cooling air required by the water-radiator to pass therethrough. In consequence of this, the acoustic result which can be achieved in this manner is disappointingly low and confined to a noise abatement of the order of no more than approximately 5 decibels (A). However, even this modest result is achieved only on condition that an air-resonance-absorbing interior lining is fitted in the encapsulation.
Other conventional constructions of a similar type are slightly more effective in acoustic respects because sound-suppressors are provided at the cooling-air intake and outlet ports, but in view of the large volume of cooling air required by the radiator, these take up a great deal of additional space and create considerable additional dynamic resistance to the flow of cooling air.
There have also been quite a number of steps and provisions of a different kind for reducing the noise of motor vehicle engines. For example, German Pat. No. 1,127,733 describes a sound resonance and vibration insulation for a motor car engine which is achieved by filling the entire engine space or compartment between the engine bonnet and the engine parts which constitute sound and vibration emission sources with foamed or expanded plastics material. However, in this arrangement the high heat retention of thermal insulation of the foamed plastic material constitutes a serious disadvantage because it markedly impairs the exchange of heat between the engine and its surroundings.
It is also familiar practice to insulate the interior of a motor vehicle relative to the engine area by means of a sound and/or heat insulating partition wall or bulkhead. As a rule this is done with the aid of multi-layered panels such as laminates with appropriate insulation layers, as described, for example in French Pat. No. 795,337 and U.S. Pat. No. 1,845,444. Obviously these provisions have no influence whatsoever with regard to noise emanation from the engine or engine-gearbox unit to the outside.
From French Pat. Nos. 934,538 and 934,539 it is further known to reduce the noise level in the passenger compartment of a motor vehicle by means of a separate bodyresonance insulating mounting of the engine-gearbox unit and an elastic suspension of the car body from the chassis of the vehicle. However, these arrangements do not include any sound-suppressing provisions for the engine as such.
Finally, German Pat. No. 1,180,155 discloses an arrangement wherein the engine area or compartment of a motor vehicle is lined with sound-absorbing panels which are provided with a profiled sealing strip of soft PVC embracing the panel edges. The purposes of this arrangement is to achieve an elastic relative mobility for the individual walls and to avoid the transmission of vibrations from one wall to an adjacent wall.
It is the aim of the present invention to obviate the disadvantages appertaining to the above-mentioned conventional arrangements and to provide a motor vehicle of the kind specified, comprising a noise-suppressingly encapsulated engine or engine-gearbox unit supported via elastic intermediate elements from the two longitudinal subframe beams of the vehicle and a fan-cooled water radiator, which ensures a high degree of acoustic efficiency for the sound suppressing encapsulation. In addition there is a noticeable weight reduction, as well as lowering of costs and an achievement of substantially simplified assembly conditions in case of service and repair work as compared with conventional arrangements.